Urea Synthesis Research Articles

Multi-functional Acyl Urea Compounds: A Review on Related Patents, Clinical Trials, and Synthetic Approaches

: Acyl ureas are a well-known class of organic compounds that have drawn a lot of attention recently because of their array of chemical properties and possible multi-use in medicine. The article summarizes the synthetic procedures used to produce various Acyl urea synthons and includes instances of clinical trials, patents, and commercialized medications having Acyl urea and N-acyl urea moiety. This extensive study examines and summarizes research on acyl urea derivatives conducted over the last 20 years from a variety of sources, including PubMed, Google Scholar, and Google Websites. When it comes to the discovery of new chemicals, urea derivatives still require attention compared to other acyl compounds. This review paper aims to provide a comprehensive overview of the various synthetic approaches utilized in the design of an array of acyl ureas to accomplish the same goal. This work summarizes information related to several heteroatom-fused acyl urea compounds, which fortunately will be a very useful resource for chemists and scientists who are interested in acyl urea synthesis and its applications in chemistry.

Recent Advances in Urea Electrocatalysis: Applications, Materials and Mechanisms†

Comprehensive SummaryUrea plays a vital role in human society, which has various applications in organic synthesis, medicine, materials chemistry, and other fields. Conventional industrial urea production process is energy−intensive and environmentally damaging. Recently, electrosynthesis offers a greener alternative to efficient urea synthesis involving coupling CO2 and nitrogen sources at ambient conditions, which affords an achievable way for diminishing the energy consumption and CO2 emissions. Additionally, urea electrolysis, namely the electrocatalytic urea oxidation reaction (UOR), is another emerging approach very recently. When coupling with hydrogen evolution reaction, the UOR route potentially utilizes 93% less energy than water electrolysis. Although there have been many individual reviews discussing urea electrosynthesis and urea electrooxidation, there is a critical need for a comprehensive review on urea electrocatalysis. The review will serve as a valuable reference for the design of advanced electrocatalysts to enhance the electrochemical urea electrocatalysis performance. In the review, we present a thorough review on two aspects: the electrocatalytic urea synthesis and urea oxidation reaction. We summarize in turn the recently reported catalyst materials, multiple catalysis mechanisms and catalyst design principles for electrocatalytic urea synthesis and urea electrolysis. Finally, major challenges and opportunities are also proposed to inspire further development of urea electrocatalysis technology. Key ScientistsFor urea electrosynthesis, Furuya et al. firstly investigated the electrochemical coreduction of CO2 and NO3−/NO2− using gas‐diffusion electrodes in 1995. Then, Wang et al. effectively achieved C—N bond formation and urea synthesis on PdCu alloy nanoparticles in 2020. Shortly, Yan and Yu et al. proposed the formation of *CO2NO2 from *NO2 and *CO2 intermediates at early stage on In(OH)3 electrocatalyst in 2021, and employed defect engineering strategy to facilitate the *CO2NH2 protonation in 2022. Amal et al. Investigated the role that Cu‐N‐C coordination plays for both the CO2RR and NO3RR. After that, Zhang's group developed In‐based electrocatalysts with artificial frustrated Lewis pairs for urea, and they offered a systematic screening approach for catalyst design in urea electrosynthesis in 2023. And sargent et al. reported a strategy that increased selectivity to urea using a hybrid catalyst.For urea electrooxidation, Stevenson et al. investigated the effect of Sr substitution toward the urea oxidation reaction. Wang et al. provided insights into the urea electrooxidation process using a β‐Ni(OH)2 electrode and Qiao et al. elucidated a two‐stage reaction pathway for UOR in 2021.

Rectifying Heterointerface Facilitated C-N Coupling Dynamics Enables Efficient Urea Electrosynthesis Under Ultralow Potentials.

Electrocatalytic C-N coupling for urea synthesis from carbon dioxide (CO2) and nitrate (NO3-) offers a sustainable alternative to the traditional Bosch-Meiser method. However, the complexity of intermediates in co-reduction hampers simultaneous improvement in urea yield and Faradaic efficiency (FE). Herein, we developed a Cu/Cu2O Mott-Schottky catalyst with nanoscale rectifying heterointerfaces through precise controllable in-situ electroreduction of Cu2O nanowires, achieving notable FE (32.6-47.0%) and substantial yields (6.08-30.4 μmol h-1 cm-2) across a broad range of ultralow applied potentials (0 to -0.3 V vs. RHE). Operando synchrotron radiation-Fourier transform infrared spectroscopy (SR-FTIR) confirmed the formation of *CO intermediates and C-N bonds, subsequently density functional theory (DFT) calculations deciphered that the Cu/Cu2O rectifying heterointerface modulated *CO adsorption, significantly enhancing subsequent C-N coupling dynamics between *CO and *NOH intermediates. This work not only provides a groundbreaking and advanced pathway for C-N coupling, but also offers deep insights into copper-based heterointerface catalysts for urea synthesis.

Rectifying Heterointerface Facilitated C‐N Coupling Dynamics Enables Efficient Urea Electrosynthesis Under Ultralow Potentials

Electrocatalytic C‐N coupling for urea synthesis from carbon dioxide (CO2) and nitrate (NO3‐) offers a sustainable alternative to the traditional Bosch‐Meiser method. However, the complexity of intermediates in co‐reduction hampers simultaneous improvement in urea yield and Faradaic efficiency (FE). Herein, we developed a Cu/Cu2O Mott‐Schottky catalyst with nanoscale rectifying heterointerfaces through precise controllable in‐situ electroreduction of Cu2O nanowires, achieving notable FE (32.6‐47.0%) and substantial yields (6.08‐30.4 μmol h‐1 cm‐2) across a broad range of ultralow applied potentials (0 to ‐0.3 V vs. RHE). Operando synchrotron radiation‐Fourier transform infrared spectroscopy (SR‐FTIR) confirmed the formation of *CO intermediates and C‐N bonds, subsequently density functional theory (DFT) calculations deciphered that the Cu/Cu2O rectifying heterointerface modulated *CO adsorption, significantly enhancing subsequent C‐N coupling dynamics between *CO and *NOH intermediates. This work not only provides a groundbreaking and advanced pathway for C‐N coupling, but also offers deep insights into copper‐based heterointerface catalysts for urea synthesis.

An agroecological approach to preparation and use of a milk protein production baseline.

Commercial dairy production occurs in a complex management environment, but increasingly, the dairy manager is expected to provide detailed reporting of productivity and environmental outcomes, for which conventional research methods double-blind crossover or case:control trials are inappropriate. This paper demonstrates the development of a milk protein production monitoring tool using a temporal (baseline) control in longitudinal, census-type investigations of modulation of system performance in response to factor change. It utilises farm-derived current and historical data, and contrasts seasonal responses with those achieved on neighbouring farms in a 2×2 contingency table. The approach is then shown to be useful in assessing the effect of two approaches to moderating milk urea concentration. Firstly, milk urea content can be monitored as it falls due to reduced feed protein content, and this fall can be arrested when milk protein content starts to decline relative to the value expected for the herd at any lactation stage. Secondly, by providing a dietary intervention aimed at increasing the availability of metabolic energy in the last month before calving, udder development can be augmented, leading to greater protein secretion capacity, meaning greater utilisation of circulating amino acids, and thus more limited substrate for urea synthesis. Thus, the changing impact of differing nutrition practices on dairy herd nitrogen excretion to environment can be followed with daily precision. In principle this approach can provide useful insights into a wide range of practical management interventions.

Theoretical Design of the Electrocatalytic Urea Synthesis from Carbon Dioxide and Nitric Oxides

Theoretical Design of the Electrocatalytic Urea Synthesis from Carbon Dioxide and Nitric Oxides

Rational Linker Design for Enhanced Performance of MOF-Derived Catalysts in Electrochemical Urea Synthesis.

2D metal-organic frameworks (2D MOFs) offer promising electrocatalytic potential for urea synthesis, yet the underlying reaction mechanisms and structure-activity relationships remain unclear. Using Cu-BDC as a model, density functional theory (DFT) calculations to elucidate these aspects are conducted. The results reveal a novel coupling mechanism involving *NO─CO and *NO─*ONCO, emphasizing the impact of linker modifications on Cu spin states and charge distribution. Notably, Cu-BDC-NH2 and Cu─BDC─OH emerge as promising catalysts. Additionally, structure-activity relationships through descriptors like d-band center, IE ratio, and L(Cu─O), providing insights for rational catalyst design is established. These findings pave the way for optimized catalysts and sustainable urea production, opening avenues for future research and technological advancements.

Dual Electron Donating Metal‐Boron Reaction Center Boosts Electrocatalytic Urea Synthesis from N2 and CO2

AbstractUrea (NH2CONH2) production by electrosynthesis at mild conditions has been hampered due to the lack of systematic evaluation of pathways in effectively activating inert N2 and CO2 molecules and facilitating the formation of C−N bonds. In this work, we evaluated 16 transition metal (M) atoms anchored on carbon nitride nanosheet with boron (B) doping (M−B@C2N) for boosting urea production by theoretical calculations. All possible urea synthesis pathways, (i) CO2 pathway, (ii) OCOH pathway, (iii) CO pathway, and (iv) NCON pathway, were comparatively studied on Cu, Fe, Co, Ni−B@C2N. This systematic calculation identified that the first reduction of *N2 is the key step for urea synthesis. We found that the bond index of *N2 shows a strong correlation with ΔG*N2→*NNH, so they are promising descriptors for screening. Through the screening, we found that Nb‐ and Mo−B@C2N show a low limiting potential of −0.56 and −0.53 V. Although previous studies found that spin could promote C−C bond formation on M−B@C2N, we found that for C−N coupling, such effects by spin were only active for Nb−B@C2N. Combining boron and early transition metal atoms allows for neighboring reaction sites that simultaneously donate electrons to activate inert N2 and CO2 for efficient urea synthesis.

Rate expression model from thermodynamics application and optimal kinetic parameters determination for urea synthesis and production process

Urea, an essential organic fertilizer, enhances soil fertility by providing 0.466 nitrogen for maximum crop yield. In this study, urea is synthesized from NH3 and CO2 in an equilibrium reaction process adhering to Le Chatelier's principle, maintained under process conditions: flow rate of 63.5 kg/s, temperature of 184 °C, and pressure of 160 kg/cm2. A new rate expression model, formulated in terms of extent of reaction and mole fraction, was developed based on mass action relations and thermodynamic models. Two industrial reactors were considered: a plug flow reactor (PFR) at Notore and a continuous stirred tank reactor (CSTR) at Indorama plants. Transient reactor models, based on material and energy balance conservation principles, were numerically resolved using MATLAB version 2020 with specified input conditions. A non-linear regression statistical optimization model was employed to refine kinetic parameter values, ensuring optimal and high-quality urea yield. Model validations were conducted using literature data, revealing higher urea yields of 0.726 and 0.7032 for the CSTR and PFR, respectively. Deviations (0.134, 0.10 to 1.135 and 0.635, 0.326 to 0.850) and root mean square errors (RMSE) (0.043, 0.033 to 0.193 and 0.137, 0.087 to 0.162) were observed when validated against plant and literature values for the CSTR and PFR respectively. The refined kinetic parameters (activation energies, Arrhenius constants, and rate constants) exhibited negligible deviations (0.0004–0.0466 and 0.0004 to 0.0491) and RMSE (0.0228, 0.0055, and 0.0256 and 0.0241, 0.0096, and 0.0269) when validated against plant data, significantly enhancing urea yield in CSTR and PFR reactors respectively.

356 Exploring the manganese requirement of feedlot steers

Abstract Angus-cross steers [n = 144; body weight (BW) = 359 kg ± 13.4] were used to assess the effect of dietary Mn and steroidal implants on trace mineral (TM) status, and liver and serum metabolites related to N metabolism. Steers (n = 6/pen) were stratified by BW in a 3 × 2 factorial. GrowSafe bunks recorded individual feed intake (experimental unit = steer; n = 24/treatment). Dietary treatments included (MANG; 8 pens per treatment; Mn as MnSO4): 1) no supplemental Mn (analyzed 14 mg Mn/kg DM; Mn0); 2) 20 mg supplemental Mn/kg DM (Mn20); 3) 50 mg supplemental Mn/kg DM (Mn50). Within MANG, steers received a steroidal implant treatment (IMP) on d 0: 1) no implant; NO; or 2) combination implant (Revalor-200; REV). Liver biopsies for TM analysis and qPCR, and blood for serum urea-N (SUN) analysis were collected on d 0, 20, 40, and 77. Liver TM, serum metabolite, enzyme activity, and gene expression data were analyzed as repeated measures using PROC MIXED of SAS 9.4. The Correlation Procedure of SAS 9.4 was utilized to assess correlations between liver arginase activity, SUN concentrations, and liver Mn concentrations. No MANG × IMP effects were noted (P ≥ 0.12) for growth or carcass measures. Steroidal implants increased final BW (FBW), overall average daily gain (ADG), and gain to feed (G:F; P ≤ 0.01). Dietary Mn did not influence FBW, overall ADG, or overall G:F (P ≥ 0.14). Liver Mn concentration increased with supplemental Mn (P = 0.01). An IMP × DAY effect was noted for liver Mn (P = 0.01) where NO and REV were similar on d 0 but NO cattle increased liver Mn from d 0 to 20 while REV liver Mn decreased. Relative expression of liver Mn transporter ZnT10 tended to be least (MANG; P = 0.10) in Mn20 while Mn0 and Mn100 were similar. Relative expression of liver Mn transporter ZIP8 was not influenced by MANG, IMP, or MANG × IMP (P ≥ 0.23). Liver arginase activity was not influenced by MANG, IMP, MANG × DAY, IMP × DAY, or MANG × IMP (P ≥ 0.15) but tended to decrease over time (DAY; P = 0.10). On d 0, 20, and 40, arginase activity was correlated (r ≤ 0.33; P ≤ 0.01) with SUN and liver Mn. Relative expression of MnSOD in the liver was greater in REV (P = 0.03) compared with NO and within a MANG × IMP effect (P = 0.01) REV increased liver MnSOD activity. This study indicates current NASEM Mn recommendations are adequate to meet demands of finishing beef cattle given a steroidal implant. This study also reveals how implants and supplemental Mn influence liver enzyme activity and genes related to arginine metabolism, urea synthesis, antioxidant capacity, and TM homeostasis.

Promoting Electrocatalytic Reduction of CO2 and Nitrate to Urea on N-Doped Porous Hollow Carbon Spheres.

The electrocatalytic coreduction of CO2 and nitrate is a green method for urea synthesis, mitigating CO2 emission and nitrate contamination. However, its slow kinetics and high energy barrier result in a poor urea production performance. Herein, we reported N-doped porous hollow carbon spheres (N-PHCS) for promoting CO2 and nitrate conversion to urea via nanoconfinement and N-doping from both reaction kinetics and thermodynamics. A high urea yield of 12.0 mmol h-1 gcat-1 with Faradaic efficiency of 19.1% was achieved on N-PHCS at -1.0 V (vs Ag/AgCl), which was comparable to or even higher than those of metal-based electrocatalysts reported. The experimental and theoretical calculation results revealed that carbon spheres with an appropriate interior void and pore size were favorable for confining reactants and intermediates to accelerate urea production, while N-doping can reduce the energy barrier for urea synthesis. By regulating the microstructure and N doping of N-PHCS, it showed a superior performance for urea electrosynthesis. The energy favorable pathway for urea synthesis was through the C-N coupling reaction of *NO and *CO, and pyridinic N can reduce the reaction energy barrier.

Mechanistic studies on defective hBN-supported metal-nonmetal synergistic catalysis for urea electrosynthesis

This study explores electrocatalytic urea synthesis promoted by a newly-designed bimetallic-tricenter catalyst consisting of defective hexagonal boron nitride (hBN) and embedded dimerized 3d metal, by means of density functional theory calculations. Among all candidates, Mn was proved to be the most feasible catalytic center originating from its unique electronic structure and metal-support interactions. The metal-nonmetal synergistic effects of the Mn2N center effectively drive site-selective co-adsorption of CO and NO, spontaneous C-N coupling, low-energy-demand NO hydrogenation, and adequate protection of the carbonyl group, achieving highly active and selective urea production. The calculated limiting potential of urea formation is as low as −0.19 V, making it more favorable energetically compared to other competing reactions such as hydrogen evolution and NO reduction reactions.

Deprotective Lossen rearrangement: a direct and general transformation of Nms-amides to unsymmetrical ureas.

Ureas stand out as potent pharmacophores in drug development, rendering them a prime focus for synthesis. Herein, we present an appealing entry point for urea synthesis from protected amines (Nms-amides) and relying on a Lossen-type rearrangement process as an elegant example of deprotective functionalisation. The method developed exhibits an exceptionally broad tolerance towards various protected amines, encompassing numerous drug derivatives, and delivers high reaction yields.

Atomic Defects Engineering Boosts Urea Synthesis toward Carbon Dioxide and Nitrate Coelectroreduction.

The atomic defect engineering could feasibly decorate the chemical behaviors of reaction intermediates to regulate catalytic performance. Herein, we created oxygen vacancies on the surface of In(OH)3 nanobelts for efficient urea electrosynthesis. When the oxygen vacancies were constructed on the surface of the In(OH)3 nanobelts, the faradaic efficiency for urea reached 80.1%, which is 2.9 times higher than that (20.7%) of the pristine In(OH)3 nanobelts. At -0.8 V versus reversible hydrogen electrode, In(OH)3 nanobelts with abundant oxygen vacancies exhibited partial current density for urea of -18.8 mA cm-2. Such a value represents the highest activity for urea electrosynthesis among recent reports. Density functional theory calculations suggested that the unsaturated In sites adjacent to oxygen defects helped to optimize the adsorbed configurations of key intermediates, promoting both the C-N coupling and the activation of the adsorbed CO2NH2 intermediate. In-situ spectroscopy measurements further validated the promotional effect of the oxygen vacancies on urea electrosynthesis.

A Strongly Coupled Metal/Hydroxide Heterostructure Cascades Carbon Dioxide and Nitrate Reduction Reactions toward Efficient Urea Electrosynthesis

The direct coupling of nitrate ions and carbon dioxide for urea synthesis presents an appealing alternative to the Bosch–Meiser process in industry. The simultaneous activation of carbon dioxide and nitrate, however, as well as efficient C–N coupling on single active site, poses significant challenges. Here, we propose a novel metal/hydroxide heterostructure strategy based on synthesizing an Ag‐CuNi(OH)2 composite to cascade carbon dioxide and nitrate reduction reactions for urea electrosynthesis. The strongly coupled metal/hydroxide heterostructure interface integrates two distinct sites for carbon dioxide and nitrate activation, and facilitates the coupling of *CO (on silver, where * denotes an active site) and *NH2 (on hydroxide) for urea formation. Moreover, the strongly coupled interface optimizes the water splitting process and facilitates the supply of active hydrogen atoms, thereby expediting the deoxyreduction processes essential for urea formation. Consequently, our Ag‐CuNi(OH)2 composite delivers a high urea yield rate of 25.6 mmol gcat.–1 h–1 and high urea Faradaic efficiency of 46.1%, as well as excellent cycling stability. This work provides new insights into the design of dual‐site catalysts for C–N coupling, considering their role on the interface.

Tuning the interfacial reaction environment via pH-dependent and induced ions to understand C–N bonds coupling performance in NO3− integrated CO2 reduction to carbon and nitrogen compounds over dual Cu-based N-doped carbon catalyst

Dual atomic catalysts (DAC), particularly copper (Cu2)-based nitrogen (N) doped graphene, show great potential to effectively convert CO2 and nitrate (NO3−) into important industrial chemicals such as ethylene, glycol, acetamide, and urea through an efficient catalytical process that involves C–C and C–N coupling. However, the origin of the coupling activity remained unclear, which substantially hinders the rational design of Cu-based catalysts for the N-integrated CO2 reduction reaction (CO2RR). To address this challenge, this work performed advanced density functional theory calculations incorporating explicit solvation based on a Cu2-based N-doped carbon (Cu2N6C10) catalyst for CO2RR. These calculations are aimed to gain insight into the reaction mechanisms for the synthesis of ethylene, acetamide, and urea via coupling in the interfacial reaction micro-environment. Due to the sluggishness of CO2, the formation of a solvation electric layer by anions (F−, Cl−, Br−, and I−) and cations (Na+, Mg2+, K+, and Ca2+) leads to electron transfer towards the Cu surface. This process significantly accelerates the reduction of CO2. These results reveal that *CO intermediates play a pivotal role in N-integrated CO2RR. Remarkably, the Cu2-based N-doped carbon catalyst examined in this study has demonstrated the most potential for C–N coupling to date. Our findings reveal that through the process of a condensation reaction between *CO and NH2OH for urea synthesis, *NO3− is reduced to *NH3, and *CO2 to *CCO at dual Cu atom sites. This dual-site reduction facilitates the synthesis of acetamide through a nucleophilic reaction between NH3 and the ketene intermediate. Furthermore, we found that the I− and Mg2+ ions, influenced by pH, were highly effective for acetamide and ammonia synthesis, except when F− and Ca2+ were present. Furthermore, the mechanisms of C–N bond formation were investigated via ab-initio molecular dynamics simulations, and we found that adjusting the micro-environment can change the dominant side reaction, shifting from hydrogen production in acidic conditions to water reduction in alkaline ones. This study introduces a novel approach using ion-H2O cages to significantly enhance the efficiency of C–N coupling reactions.

Unusual C-N coupling mechanism via NO dimerization for the electrochemical synthesis of urea on transition metal dimers supported by two-dimensional expanded phthalocyanine

Electro-synthesis of urea is a powerful alternative to traditional demanding industrial engineering by selective reduction of N2 and CO2. Due to the existence of inert NN bond, usual C-N coupling has always hindered the design and performance of catalysts. Herein, we present an unusual C-N coupling mechanism for highly electrochemical catalytic synthesis of urea via NO dimerization on transition metal dimers supported by two-dimensional expanded phthalocyanine (TMTM-Pc) as a prototype through first principles calculations. The key is that the adsorbed *NO dimer can directly jump over challenging step of N-N bond breaking and associate with CO. Particularly, FeFe-Pc is singled out in terms of activity, selectivity, and stability via proposed reaction pathways. What's more, we discovered an easy descriptor, namely, the difference of the adsorption energies of *NO-CO-NO* and *NO-NO*, ∆E(*NO-CO-NO* - *NO-NO*), to consummately depict the thermal-kinetic relationships for the C-N coupling. This work may broaden the understanding of urea formation mechanism and provide more options for future research.

Promising urea electrosynthesis by C-N coupling on copper-based single-atom alloys

Electrochemical synthesis of urea holds a significant importance in the energy landscape, however, the lack of efficient electrocatalysts is the main bottleneck. In this study, 40 single-atom alloys (SAAs) based on Cu(100) and Cu(111) surfaces have been systematically investigated as electrocatalysts for CO2 and N2 co-reduction to produce urea utilizing first-principles calculations. A promising single N and C coupling pathway is uncovered on Cu-based SAAs, besides conventional NCON, CO2, COOH, and CO pathways. CuHf(100) displays a high efficiency in N-N decomposition, C-N coupling, and low reaction limiting potential. Furthermore, CuHf(100) and CuSc(100) have been identified as superior electrocatalysts for efficient urea electrosynthesis. This work provides potential reaction mechanisms with specific single N species, but also a universal strategy for the surface engineering of transition metal-based catalysts in electrocatalytic urea synthesis reactions.

Comparative analysis of eight urea-electricity-heat-cooling multi-generation systems: Energy, exergy, economic, and environmental perspectives

The Haber-Bosch process for urea production is known for its significant carbon emissions. While the chemical looping ammonia generation method presents a potential alternative, its technical and economic feasibility still requires further investigation. This paper conducts a comparative analysis of eight renewable energy-driven urea-electricity-heat-cooling multi-generation systems by developing their energy, exergy, economic, and environmental evaluation models. Considering the fluctuation in renewable energy resources, an annual evaluation of the different systems is conducted based on a monthly time scale. The results indicate that systems based on the Haber-Bosch process have higher average energy and exergy efficiencies of 60–80 % and 40–50 %, respectively. For the chemical looping ammonia generation process, the respective efficiencies are 50–70 % and 30–40 %. Additionally, the system integrating the Haber-Bosch reaction, reduction reactor, and solid oxide fuel cell yields the highest energy and exergy efficiencies among the eight systems, at 68.2 % and 45.78 %, respectively. However, it is inferior to the multi-generation system integrating the chemical looping ammonia generation process in terms of economic and environmental performance. In addition, the system integrating the chemical looping ammonia generation process and solid oxide fuel cell has the shortest discounted payback period of 8 years, with annual revenue and net present value of 32.63 and 11.66 MUSD, respectively. While the operating expenditures of the Haber-Bosch (12.6–15.7 MUSD) are lower than those of the chemical looping ammonia generation process (14.0–17.5 MUSD), its capital expenditures (382.0–410.8 MUSD) are significantly higher than those of the chemical looping ammonia generation process (302.4–307.3 MUSD). Furthermore, the conducted environmental evaluation shows that the multi-generation system integrating the chemical looping ammonia generation process and reduction reactor exhibits lower overall carbon emissions (0.013 t CO2/t urea) compared to the state-of-the-art method of oxy-fuel coal-fired power plant for urea synthesis.

Enhanced solar urea synthesis from CO2 and nitrate waste via oxygen vacancy mediated-TiOx support lead-free perovskite

The nitrogen fertilizer industry, particularly urea production, notably contributes to greenhouse gas emissions and energy consumption. Urea synthesis via solar energy encounters several challenges. Specifically, solar urea synthesis methods often exhibit low efficiency and yield, primarily stemming from inefficient energy conversion processes and intricate reaction pathways. Moreover, the kinetics of the urea synthesis reaction may be sluggish, thereby impacting the overall production rate. Therefore, in this study, we introduce a novel electron-reserve-enhanced Cs2CuBr4/TiOx-Ar (CCBT-Ar) structure for the photocatalytic synthesis of urea from CO2 and nitrate waste. Theoretical calculations and spectroscopic analysis underscore the critical role of oxygen vacancies (Ov) within the amorphous TiOx shell, enhancing reactant adsorption and catalyzing the rate-determining step (*OCONH2→*HOCONH2). However, the presence of Ov also results in significant carrier recombination, acting as trapping centers and reducing urea production activity. Importantly, we demonstrate that in-situ-grown carbon nanosheets, in conjunction with TiOx, function as efficient electron reservoirs, markedly mitigating trapping-induced recombination and facilitating electron redistribution. These reserved electrons can then actively participate in the urea synthesis process. As a result, the electron-reserve-enhanced structure exhibits robust solar urea yield and selectivity, even in challenging wastewater conditions. This work provides a rational and innovative approach to catalyst development in complex solar synthesis, offering promising avenues for the sustainable production of value-added chemicals while concurrently reducing carbon emissions.